A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.

learn more… | top users | synonyms (1)

2
votes
4answers
203 views

Are empty black holes possible

When just considering GR without evaporation nor QM, is an empty (containing no matter or anything) black hole possible ? Let's say that there is only GR and nothing else (no matter or boson fields), ...
1
vote
0answers
306 views

Interstellar Movie: Black hole shown in the movie [duplicate]

In the interstellar movie, the black hole shown has a ring of light orbiting around it. From what I know, (correct me if I'm wrong) that light is unable to escape the gravity of the blackhole and ...
3
votes
1answer
176 views

Could Hyper-Massive Black Holes be due to Dark Matter in the Early Universe?

An interesting discussion started here: Is there a limit as to how fast a black hole can grow? I am curious if Thompson Scattering and Eddington Luminosity have the same effect on Dark Matter (or ...
0
votes
3answers
119 views

What is the reasoning behind the idea that light cannot escape from a black hole? [duplicate]

According to the definition, light cannot escape from a black hole. How did scientists deduce that light cannot escape from a black hole?
8
votes
5answers
2k views

Why aren't all black holes the same “size”?

The center of a black hole is a singularity. By definition, a singularity has infinite density. So how can a black hole with a different mass or density be described?
12
votes
3answers
18k views

How do we determine the mass of a black hole?

Since by definition we cannot observe black holes directly, how do astronomers determine the mass of a black hole? What observational techniques are there that would allow us to determine a black ...
0
votes
1answer
221 views

What is the speed of light after it has entered a black hole?

I was just thinking about this the other day. Given Einstein's Relativity etc. assigning the cosmic "speed limit" the value of $c=299792458\:\frac{m}{s}$, we know that the event horizon is the point ...
4
votes
1answer
302 views

Is dark energy around a black hole locally curved?

The repartition of dark energy in the vacuum is homogeneous all over the universe. The diagram below represents space with a black hole in the middle. The square is divided in small unit squares. If ...
1
vote
2answers
99 views

Are black holes hot?

If no light can escape black holes, in my mind they would act as a greenhouse, collecting radiation from the stars or CMB or anything. Or is all this energy just absorbed by the black hole?
1
vote
2answers
249 views

Can a sufficiently large black hole be singularity-free?

This came to me after reading that a black-hole that has the mass of the observable universe will also have an event horizon that covers the observable universe. Since the definition of a black hole ...
4
votes
2answers
1k views

Where does information go if thermodynamic death?

Often read that until Hawking the black holes were introducing a problem with information. Allegedly information should be unable disappear, while this was happening in classic black holes. What ...
0
votes
2answers
202 views

How can Maxwell's Demon erase information while a black hole can not?

It is stated, that information can't disappear even in black holes. On the other hand, it is stated, that mystic beings, like Maxwell demons, can easily erase any information if they just pay with ...
1
vote
2answers
75 views

Would a black hole's rotational axis precess in orbit around the sun?

The earth rotates, and its axis of rotation precesses due to the gravitational pull of the sun and moon and other planets upon the mass of the earth. If an earth-sized, rotating black hole was in ...
1
vote
0answers
209 views

Boyer–Lindquist coordinates

In the Kerr solution to the vacuum Einstein Equation written in Boyer–Lindquist coordinates. Because it is not spherical polar coordinates, $r$ ranges from 0 to infinity does not cover all the space, ...
3
votes
0answers
70 views

Is the $\alpha'$ expansion in string theory an asymptotic expansion?

The low-energy bosonic effective actions of string theory lead to Einstein-Hilbert gravity, along with scalars and $p$-form Maxwell fields. For example, the action for type IIA string theory is $S = ...
-1
votes
3answers
440 views

Are electrons miniature black holes? [duplicate]

For something to be a blackhole, it must have gravity and the radius must be smaller than the schwarzschild radius for its mass. -Electrons have gravity -Electron are theoretically believed to be ...
0
votes
1answer
91 views

How dense and compact would Kepler-5b need to be to become a black hole

How dense and compact does Kepler-5b need to be to become a black hole ?
1
vote
1answer
48 views

Calculation, radius of Saggriatus A* (SMBH) , Error in Wikipedia?

The parameter Schwarzschild Radius of Saggriatus A* is given in Wiki by 2.08×1015 (~0.2 ly) see in Parameters http://en.wikipedia.org/wiki/Schwarzschild_radius However, when I do the calculation ...
2
votes
2answers
996 views

Spacetime geometry around two black holes

For space-time geometry we all know images like he one below. But if I were to take a neutron star and put it right next to but not touching a black hole what effect would that have on the geometry of ...
1
vote
2answers
108 views

Pumping charged particles (of same charge) into a blackhole

Would would happen if you started pumping charged particles of same charge into a black hole? Let's assume that you have an infinite number of those charged particles. What will happen to the event ...
0
votes
0answers
95 views

Topology of a black hole

How many dimensions are theorized for a black hole, in view of the fact that black holes are not observed directly.
0
votes
1answer
70 views

The ever increasing pull of a black hole

If something is caught in the pull of a black hole and keeps accelerating it can't keep accelerating with no limits or else it would accelerate beyond c. So is there a limit on how fast acceleration ...
21
votes
4answers
3k views

What does this depiction of a black hole in the movie Interstellar mean?

I was expecting a whirlpool in 3D and the matter glowing from friction as it nears the center, as I expected a event horizon to be negligible visually. How does this depiction work? How big is the ...
2
votes
1answer
1k views

Why does the Ricci tensor vanishes in Schwarzschild metric? [duplicate]

If the Schwarzschild metric is suppose to describe the behaviour of a spherical object in flat space, so the Schwarzschild is different from the flat metric because it describes curved space so why ...
7
votes
2answers
2k views

Do neutrinos of any flavor get trapped in black holes?

This question has been bothering me a bit. I know that neutrinos have super small mass and they interact via the weak force. Since they have a non-zero mass, they should be affected by black holes and ...
0
votes
2answers
226 views

How could the “Big Bang” singularity have actually expanded? [duplicate]

We have mountains of evidence about singularities and how they work, and we have mountains of evidence that the "Big Bang" was the origin of the universe as we know it. But if compressing enough ...
0
votes
1answer
42 views

Why can't no particle rotate opposite to the central mass within the ergosphere?

Wiki says about the Kerr metric: A moving particle experiences a positive proper time along its worldline, its path through spacetime. However, this is impossible within the ergosphere, where ...
13
votes
4answers
991 views

Big Bang snuffed by a black hole?

Wasn't the density of the universe at the moment after the Big Bang so great as to create a black hole? If the answer is that the universe/space-time can expand anyway what does it imply about what ...
1
vote
1answer
111 views

White Hole Formation and Queries

How do white holes form? Why are they called the "time-reversed" versions of a black hole? What's an "eternal" black hole? How come a white hole is only encountered if you remove the star from the ...
1
vote
2answers
279 views

What am I missing in this thought experiment about a black hole?

I've got a problem setting up a general relativity (GR) thought experiment. Thanks for your help! I'm the observer, in a lab that is falling through the event horizon of a black hole, observing a ...
4
votes
2answers
179 views

How close can an observer approach the black hole in an unpowered flyby without falling into it?

In classical mechanics by choosing the right trajectory you can approach a planet arbitrarily closely, if there is no atmosphere or anything to slow you down, you can approach the surface then fly ...
21
votes
5answers
3k views

Why singularity in a black hole, and not just “very dense”?

Why does there have to be a singularity in a black hole, and not just a very dense lump of matter of finite size? If there's any such thing as granularity of space, couldn't the "singularity" be just ...
1
vote
1answer
112 views

White Hole Formation [duplicate]

How does a white hole form in nature if it were to exist? No knowledge of general relativity or advanced mathematics but doing a researching a physics project and need a basic explanation.
3
votes
3answers
213 views

Really nothing special when falling into a black hole?

It has been said time and again, that an observer who falls into a black hole will not notice anything special. Is this really true? There is of course the problem with the tidal forces, but I ...
4
votes
1answer
286 views

No hair theorem and black hole entropy

The no hair theorem says that black holes rapidly converge to a state that is completely described just by their mass, spin and charge. Black hole thermodynamics says that the black hole entropy is ...
5
votes
1answer
359 views

Does compression of matter increase gravity?

Black holes are thought to originate when a star burns out and collapses to a smaller physical size. This compresses it's matter, but would that increase it's gravity? And would it be enough to ...
0
votes
1answer
104 views

Hawking radiation (black hole evaporation) [duplicate]

I understand that one of the simplified ways of looking at Hawking radiation is a pair of virtual particles close to the event horizon (but outside of it). The particle with negative energy falls into ...
7
votes
1answer
135 views

Should all theories of gravity have Schwarzschild solution?

A consistent theory of gravity must include the Newton's classical theory of gravity as a weak field approximation. Moreover, to satisfy the experiments in the solar system, the Schwarzschild ...
0
votes
1answer
83 views

Can a free falling observer localize the event horizon by calculations?

I'm think that in general relativity we can always pass the one curve in one coordinate system for another coordinate system. My intuition say that the free falling observer locate the event horizon ...
0
votes
1answer
51 views

Schwarzschild Solution Convention

In looking at the components of the Schwarzschild Metric, one finds $ g_{00} = (1 - \frac{r_s}{r})c^2 $. Wikipedia states that $r$ is measured as the circumference, divided by $2π$, of a sphere ...
0
votes
1answer
67 views

Is a black hole really a hole in space? [closed]

What if when a supernova occurs, instead of it condensing into a singularity it creates enough force to tear a hole into the fabric of space? Is a black hole just what is sounds like, a hole in space? ...
0
votes
1answer
77 views

Paradox of nesting black holes and release of energy

By dumping a gas cloud into a small black hole, I can produce radiation energy, this is how quasars produce energy. By dumping the previous black hole, with the gas cloud inside, into a black hole, ...
1
vote
0answers
66 views

Binary Singularity?

When two black holes collide, if the singularities were very small they would never merge together. they would rotate very fast as something other than a disk. The event horizon would oscillate very ...
6
votes
9answers
531 views

Why does my apple not weigh 500 tons?

Related to this question: What is potential energy truly? $E=mc^2$ - energy equals mass. So, if an object has gravitational potential energy relative to another object, it should have additional mass ...
2
votes
0answers
154 views

What are the equations of motion that model near light speed orbits of a massive body about incredibly massive bodies?

In Kip Thorne's recently published book, The Science of Interstellar, he describes, by means of an illustration, the complex nature of a spacecraft orbiting a massive black hole with velocities ~ ...
1
vote
3answers
418 views

Eternal Black Holes

What is the definition of an eternal black hole? Studying white holes and the term appears in relation to this field of research.
3
votes
0answers
69 views

why are chemical reactions the same at different gravity levels

Are all chemical reactions the same at a quantum level in different levels of gravity? How does the mass of subatomic particles change atomic behaviour at different gravity, in terms of speed and ...
1
vote
0answers
26 views

Evaporation of a black hole [duplicate]

What happens to the singularity within a black hole when a black hole evaporates? If there is a point in space which is both infinitely dense and small, do they simply evaporate as well?
3
votes
2answers
126 views

Does the escape velocity of a black hole exceed $c$ *before* a singularity is created?

As an offshoot of the question Can we have a black hole without a singularity? I'm curious if the point of no return at which the massive object is condemned to become a singularity happens before its ...
2
votes
0answers
45 views

How can a black hole increase mass? [duplicate]

As far as I know, the time dilation at the event horizon of a black hole is infinite, so everything falls asymptotically towards, but never reaching, the horizon for an outside observer. How then can ...